Cutting through mortises

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  • durango dude
    Senior Member
    • Mar 2011
    • 934
    • a thousand or so feet above insanity
    • 50s vintage Craftsman Contractor Saw

    Cutting through mortises

    (photos coming in a week or so - gotta charge the camera).

    Arms on my morris chair have through-mortises

    It’s no small task -----

    a) Determine overhang
    b) Draw line down the length of arm, designating inside of of tenon
    c) Draw line down length of arm, designating outside of tenon (width of tenon)
    d) Determine forward projection of arm
    e) Aligning arm with inside/outside lines – mark front of tenon
    f) Mark back of tenon
    g) Using resulting square – drill using forstner. Drill from the top of the arm to the bottom to prevent visible tear-out.
    h) Chisel down into the straight marked lines slightly to avoid tear-out
    i) Clean out the mortise with a jigsaw (be sure blade runs very straight --- always cut slightly inside the line)
    j) Straighten out mortise using chisels.
    k) Check for fit over tenon
    l) Fine tune with chisel --- sneak up on it.

    Biggest problem I have is tear-out. However, if the tear-out is on the bottom of the chair arm,, I can deal. I'm also preventing tear-out by chiseling into the mortise lines a little.

    I think a mortiser might work a little better - but I don't have one. The through mortise is 1 3/8" square. A 1" chisel works fairly well ---- as long as you pre-chisel a little.
  • Cochese
    Veteran Member
    • Jun 2010
    • 1988

    #2
    I'd almost consider a mortiser or a repeatable mortising method as a sunk cost to doing a Morris. What about a guide block?
    I have a little blog about my shop

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    • durango dude
      Senior Member
      • Mar 2011
      • 934
      • a thousand or so feet above insanity
      • 50s vintage Craftsman Contractor Saw

      #3
      My tenons aren't perfect - so I found the best way to cut the through mortises was to draw a base line ----- align the base line ---- and then trace the tenon.

      A guide block would work really well if the tenons were perfect. I found that starting with a basic round hole - and then sneaking out slowly until I nail it ----- worked the best.

      The two arms on the chair took about 1 hour each.

      Right now, I'm just glad I didn't do the bow-armed chair ----- angled through mortises would have added even more complexity to the job. The straight through-mortises are hard enough!!!

      Comment

      • JimD
        Veteran Member
        • Feb 2003
        • 4187
        • Lexington, SC.

        #4
        I've made a few through mortises for protruding tenons and didn't enjoy it. I have a little Jet hollow chisel mortiser and it still wasn't any fun. It's hard to make a mortise with really straight sides with my mortiser. I've also made fake through mortises. Shallow mortises on one side for a plug, in other words. That was a LOT easier and looks the same.

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